A conventional object detection apparatus intermittently emits a laser light and detects the laser light reflected by an obstacle such as a forward vehicle to detect a distance to the obstacle based on a time lag between the emission and the detection of the laser light.
JP2002-031685A discloses an object detection apparatus for a vehicle comprising a light emitter for emitting laser light, a pivotally-movable polygon mirror for reflecting the laser light to a scanning range in front of the vehicle, and a photoreceptor for detecting the laser light reflected by an obstacle.
The object detection apparatus, which is exposed to a harsh environment during vehicle travel, contains scanning mechanisms, optical devices, and electric circuits such as those described above in a housing to protect them from dirt, scattering stones, and water. Additionally, the housing has a light emission portion and a light reception portion that are made of a transparent material.
When the object detection apparatus is used for detecting the presence of and/or a distance to a forward obstacle, the apparatus is installed on a front face of the vehicle. Thus, the light emission and reception windows of the apparatus are often damaged by scattering stones and other loose debris commonly found on roadways.
If the object detection apparatus stops operating due to the damage, an electric control unit (ECU) turns off the apparatus and alarms a driver of the vehicle that the object detection apparatus is suffering a breakdown.
However, the object detection apparatus may continue to operate while the light emission and/or reception windows include fractures. In this case, the fractures may allow dirt and/or water to pass into the apparatus, thereby causing condensation or rust to accumulate on the devices in the apparatus. This impairs the operational performance of the apparatus such that it may cause an erroneous distance detection and/or a decrease in the detection range.